Sheath

ABSTRACT

A sheath for at least partially covering a tubular member, includes a helically wound strip having an electrically conductive portion extending through the strip from an inner surface of the strip to an outer surface of the strip. The conductive portion also extends continuously substantially helically along at least part of the length of the sheath. The sheath, and in particular the strip, may be formed from a flame retardant material.

FIELD OF THE INVENTION

The present invention relates to a sheath for at least partiallycovering a tubular member and, in particular, for covering a tubularmember of the type commonly used in an underground mine.

BACKGROUND OF THE INVENTION

It is common in underground mines to provide mining machines with tubingfor carrying hydraulic fluid or air. However, such tubing is subject toAustralian Standards which specify, among other things, that the tubingshould not exceed an average duration of flaming and glowing of thirtyseconds (ie. should be flame retardant) and the electrical resistance ofthe tubing should not be greater than 1MΩ/m.

SUMMARY OF THE INVENTION

The present invention seeks, among other things, to provide a sheathwhich, when combined with conventional tubing of the type used in anunderground mine, provides a tube assembly which satisfies the abovementioned Australian Standards requirements.

In accordance with one aspect of the present invention there is provideda sheath for at least partially covering a tubular member, the sheathincluding a helically wound strip having an electrically conductiveportion extending through the strip from an inner surface of the stripto an outer surface of the strip, the said conductive portion extendingcontinuously substantially helically along at least part of the lengthof the sheath.

BRIEF DESCRIPTION OF DRAWINGS

The present invention will now be described by way of example withreference to the accompanying drawings in which:

FIG. 1 is a diagrammatic perspective view of a sheath in accordance withthe present invention; and

FIG. 2 is a diagrammatic perspective view of a sheath in accordance withan alternative embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, there is shown a sheath 10 for covering, in use, atleast a portion of a tubular member which may be a tube carryinghydraulic fluid or air in a mine.

The sheath 10 is formed by helically winding an elongate strip 12 offlame retardant material, in this example, polyethylene, so as to forman elongate cylinder, the strip 12 being helically wound such that eachturn of the helically wound strip is spaced from an adjacent turn by agap 14. By forming the sheath 10 from a helically wound strip andproviding a gap 14 intermediate adjacent turns of the helically woundstrip, the sheath 10 is provided with sufficient flexibility to allowthe sheath 10, in use, to conform with the curvature of a portion of atube which is covered by the sheath 10.

The sheath 10 also includes an electrically conductive portion 16 whichextends from an inner surface 18 of the sheath 10 to an outer surface 20of the sheath 10. The electrically conductive portion 16 also extendshelically from a first longitudinal end 22 of the sheath 10 to a secondopposite longitudinal end (not shown) of the sheath 10. The arrangementis such that when, in use, a portion of a tube is covered by the sheath10, an electrical connection is made between an outer surface of thetube and a portion of the electrically conductive portion 16 on theinner surface 18 of the sheath 10. Since the electrically conductiveportion 16 extends continuously along the length of the sheath, itfollows that the electrical potential at the electrically conductiveportion 16 is substantially constant between the first 22 and secondlongitudinal ends of the sheath 10. Generally, in use, the electricallyconductive portion 16 and thereby the tube covered by the sheath 10 issubstantially at ground potential by virtue of an electrical connectionwhich is made by a portion of the electrically conductive portion 16 onthe outer surface 20 of the sheath 10 touching a portion of, forexample, a mining machine on which the tube is located. However, it willbe understood that, if necessary, an electrical link could be connectedbetween the electrically conductive portion and ground.

In this example, the electrically conductive portion 16 is a mixture ofhigh density polyethylene plastics material and particulate carbon, thestrip 12 being formed by coextruding the high density polyethylene andcarbon mixture with polyethylene so as to form a polyethylene striphaving an electrically conductive portion extending along the length ofthe strip. Preferably, the thickness of the electrically conductiveportion 16 is approximately 1 mm.

Where the electrically conductive portion 16 is formed of a materialwhich is flammable, the strip 12 may also include an additive materialin addition to the flame retardant material or the strip 12 may whollyconsist of a material which, when exposed to a fire situation, aids toextinguish flames emanating from the electrically conductive portion 16within 30 seconds. Halide based compounds are suitable for this purpose.

It will be appreciated that instead of forming the strip 12 and theelectrically conductive portion by a coextruding process, the helicalstrip 12 of the sheath 10 could be provided with an electricallyconductive portion in any other suitable way, for example by stitchingan electrically conductive thread along the length of the helix, theimportant aspect being that an electrical connection is made betweeninner and outer surfaces of the sheath and between the sheath 10 and thetubular member received in the sheath 10.

It will also be appreciated that the strip could include more than oneelectrically conductive portion along the length of the helical strip.However, where the electrically conductive portion is formed of amaterial which is flammable, the combined width of the outer surface 20of the conductive portion 16 of the sheath 10 should be less than thearea above which the electrically conductive portion is susceptible toresist flame extinction by a flame extinguishing material in the strip.

Furthermore, it will be appreciated that the transverse cross sectionalarea of the electrically conductive portion could be any shape, theimportant aspect being that an electrically conducting path is providedbetween the inner surface 18 and the outer surface 20 of the sheath 10.An example of an alternative embodiment of the sheath having analternative shaped electrically conducting portion is shown in FIG. 2.Like features are indicated by like reference numerals. In thisembodiment, the surface area of the conducting portion on the innersurface 18 of the sheath is greater than the surface area of theconducting portion on the outer surface 20 of the sheath. In this way,good electrical contact is ensured between the sheath and the tubularmember received in the sheath.

Modifications and variations such as would be apparent to the skilledaddressee are deemed to be within the scope of the present invention.

What is claimed is:
 1. A sheath for at least partially covering atubular member, wherein the sheath includes a helically wound striphaving an electrically conductive portion extending through the stripfrom an inner surface of the strip to an outer surface of the strip, thestrip being at least partially formed of a flame retardant material andthe conductive portion extending continuously substantially helicallyalong at least part of the length of the sheath.
 2. A sheath as claimedin claim 1, wherein the flame retardant material includes polyethylene.3. A sheath as claimed in claim 1, wherein the flame retardant materialincludes an additive material which, when the electrically conductiveportion is formed of a flammable material, aids to extinguish flamesemanating from the electrically conductive portion.
 4. A sheath asclaimed in claim 1, wherein the flame retardant material comprises ahalide compound.
 5. A sheath as claimed in claim 1, wherein theelectrically conductive portion includes polyethylene and particulatecarbon.
 6. A sheath as claimed in claim 5, wherein the polyethylene ishigh density polyethylene.
 7. A sheath as claimed in claim 1, wherein aplurality of said electrically conductive portions are provided.
 8. Asheath as claimed in claim 1, wherein transverse cross-sectional area ofthe electrically conductive portion is substantially elongaterectangular shaped.
 9. A sheath as claimed in claim 8, wherein the widthof the transverse cross-sectional area of the electrically conductiveportion is approximately 1 mm.
 10. A sheath as claimed in claim 1,wherein the transverse cross-sectional area of the electricallyconductive portion is substantially T-shaped.
 11. A sheath as claimed inclaim 1, wherein the sheath is formed by co-extruding the strip withelectrically conductive material.
 12. A sheath as claimed in claim 1,wherein the sheath is formed by stitching electrically conductivematerial into the strip.
 13. A sheath as claimed in claim 1, wherein thestrip is helically wound such that each turn of the strip is spaced froman adjacent turn by a gap.